We are using a number of glycolytic enzymes and creatine phosphokinase as well characterized enzymes to investigate the mechanisms which regulate the levels of specific proteins in animal cell. These investigations include measurements of the rates of synthesis and degradation of these enzymes in adult tissues, during embryogenesis and maturation of the tissues, and in tissue disease states such as muscular dystrophy. More detailed investigations on the specific regulatory events which control the biogenesis of these enzyme molecules are being made in cell-free protein synthesizing systems using polyribosomes, total tissue RNA, and mRNA to program protein synthesis. Results of these investigations should lead to a better understanding of the mechanisms which control the levels of specific enzymes in normal and diseased animal cells.